By inducing delays in the right places, Jann Horn created a reproducer
for a hard to hit UAF issue that became possible after VMAs were allowed
to be recycled by adding SLAB_TYPESAFE_BY_RCU to their cache.
Race description is borrowed from Jann's discovery report:
lock_vma_under_rcu() looks up a VMA locklessly with mas_walk() under
rcu_read_lock(). At that point, the VMA may be concurrently freed, and
it can be recycled by another process. vma_start_read() then
increments the vma->vm_refcnt (if it is in an acceptable range), and
if this succeeds, vma_start_read() can return a recycled VMA.
In this scenario where the VMA has been recycled, lock_vma_under_rcu()
will then detect the mismatching ->vm_mm pointer and drop the VMA
through vma_end_read(), which calls vma_refcount_put().
vma_refcount_put() drops the refcount and then calls rcuwait_wake_up()
using a copy of vma->vm_mm. This is wrong: It implicitly assumes that
the caller is keeping the VMA's mm alive, but in this scenario the caller
has no relation to the VMA's mm, so the rcuwait_wake_up() can cause UAF.
The diagram depicting the race:
T1 T2 T3
== == ==
lock_vma_under_rcu
mas_walk
<VMA gets removed from mm>
mmap
<the same VMA is reallocated>
vma_start_read
__refcount_inc_not_zero_limited_acquire
munmap
__vma_enter_locked
refcount_add_not_zero
vma_end_read
vma_refcount_put
__refcount_dec_and_test
rcuwait_wait_event
<finish operation>
rcuwait_wake_up [UAF]
Note that rcuwait_wait_event() in T3 does not block because refcount
was already dropped by T1. At this point T3 can exit and free the mm
causing UAF in T1.
To avoid this we move vma->vm_mm verification into vma_start_read() and
grab vma->vm_mm to stabilize it before vma_refcount_put() operation.
Fixes: 3104138517fc ("mm: make vma cache SLAB_TYPESAFE_BY_RCU")
Reported-by: Jann Horn <jannh(a)google.com>
Closes: https://lore.kernel.org/all/CAG48ez0-deFbVH=E3jbkWx=X3uVbd8nWeo6kbJPQ0KoUD+…
Signed-off-by: Suren Baghdasaryan <surenb(a)google.com>
Cc: <stable(a)vger.kernel.org>
---
Changes since v1 [1]
- Made a copy of vma->mm before using it in vma_start_read(),
per Vlastimil Babka
Notes:
- Applies cleanly over mm-unstable.
- Should be applied to 6.15 and 6.16 but these branches do not
have lock_next_vma() function, so the change in lock_next_vma() should be
skipped when applying to those branches.
[1] https://lore.kernel.org/all/20250728170950.2216966-1-surenb@google.com/
include/linux/mmap_lock.h | 23 +++++++++++++++++++++++
mm/mmap_lock.c | 10 +++-------
2 files changed, 26 insertions(+), 7 deletions(-)
diff --git a/include/linux/mmap_lock.h b/include/linux/mmap_lock.h
index 1f4f44951abe..da34afa2f8ef 100644
--- a/include/linux/mmap_lock.h
+++ b/include/linux/mmap_lock.h
@@ -12,6 +12,7 @@ extern int rcuwait_wake_up(struct rcuwait *w);
#include <linux/tracepoint-defs.h>
#include <linux/types.h>
#include <linux/cleanup.h>
+#include <linux/sched/mm.h>
#define MMAP_LOCK_INITIALIZER(name) \
.mmap_lock = __RWSEM_INITIALIZER((name).mmap_lock),
@@ -183,6 +184,28 @@ static inline struct vm_area_struct *vma_start_read(struct mm_struct *mm,
}
rwsem_acquire_read(&vma->vmlock_dep_map, 0, 1, _RET_IP_);
+
+ /*
+ * If vma got attached to another mm from under us, that mm is not
+ * stable and can be freed in the narrow window after vma->vm_refcnt
+ * is dropped and before rcuwait_wake_up(mm) is called. Grab it before
+ * releasing vma->vm_refcnt.
+ */
+ if (unlikely(vma->vm_mm != mm)) {
+ /* Use a copy of vm_mm in case vma is freed after we drop vm_refcnt */
+ struct mm_struct *other_mm = vma->vm_mm;
+ /*
+ * __mmdrop() is a heavy operation and we don't need RCU
+ * protection here. Release RCU lock during these operations.
+ */
+ rcu_read_unlock();
+ mmgrab(other_mm);
+ vma_refcount_put(vma);
+ mmdrop(other_mm);
+ rcu_read_lock();
+ return NULL;
+ }
+
/*
* Overflow of vm_lock_seq/mm_lock_seq might produce false locked result.
* False unlocked result is impossible because we modify and check
diff --git a/mm/mmap_lock.c b/mm/mmap_lock.c
index 729fb7d0dd59..aa3bc42ecde0 100644
--- a/mm/mmap_lock.c
+++ b/mm/mmap_lock.c
@@ -164,8 +164,7 @@ struct vm_area_struct *lock_vma_under_rcu(struct mm_struct *mm,
*/
/* Check if the vma we locked is the right one. */
- if (unlikely(vma->vm_mm != mm ||
- address < vma->vm_start || address >= vma->vm_end))
+ if (unlikely(address < vma->vm_start || address >= vma->vm_end))
goto inval_end_read;
rcu_read_unlock();
@@ -236,11 +235,8 @@ struct vm_area_struct *lock_next_vma(struct mm_struct *mm,
goto fallback;
}
- /*
- * Verify the vma we locked belongs to the same address space and it's
- * not behind of the last search position.
- */
- if (unlikely(vma->vm_mm != mm || from_addr >= vma->vm_end))
+ /* Verify the vma is not behind of the last search position. */
+ if (unlikely(from_addr >= vma->vm_end))
goto fallback_unlock;
/*
base-commit: c617a4dd7102e691fa0fb2bc4f6b369e37d7f509
--
2.50.1.487.gc89ff58d15-goog
The userprogs infrastructure does not expect clang being used with GNU ld
and in that case uses /usr/bin/ld for linking, not the configured $(LD).
This fallback is problematic as it will break when cross-compiling.
Mixing clang and GNU ld is used for example when building for SPARC64,
as ld.lld is not sufficient; see Documentation/kbuild/llvm.rst.
Relax the check around --ld-path so it gets used for all linkers.
Fixes: dfc1b168a8c4 ("kbuild: userprogs: use correct lld when linking through clang")
Cc: stable(a)vger.kernel.org
Signed-off-by: Thomas Weißschuh <thomas.weissschuh(a)linutronix.de>
Reviewed-by: Nathan Chancellor <nathan(a)kernel.org>
---
Changes in v2:
- Use plain ifdef instead of ifneq
- Rebase onto v6.16
- Pick up review tag from Nathan
- Link to v1: https://lore.kernel.org/r/20250724-userprogs-clang-gnu-ld-v1-1-3d3d071e53a7…
---
Makefile | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/Makefile b/Makefile
index 478f2004602da03c9039044e3288f24a13833cc7..7d24245d118c0e903119263b871d2e5c2759f48a 100644
--- a/Makefile
+++ b/Makefile
@@ -1134,7 +1134,7 @@ KBUILD_USERCFLAGS += $(filter -m32 -m64 --target=%, $(KBUILD_CPPFLAGS) $(KBUILD
KBUILD_USERLDFLAGS += $(filter -m32 -m64 --target=%, $(KBUILD_CPPFLAGS) $(KBUILD_CFLAGS))
# userspace programs are linked via the compiler, use the correct linker
-ifeq ($(CONFIG_CC_IS_CLANG)$(CONFIG_LD_IS_LLD),yy)
+ifdef CONFIG_CC_IS_CLANG
KBUILD_USERLDFLAGS += --ld-path=$(LD)
endif
---
base-commit: 038d61fd642278bab63ee8ef722c50d10ab01e8f
change-id: 20250723-userprogs-clang-gnu-ld-7a1c16fc852d
Best regards,
--
Thomas Weißschuh <thomas.weissschuh(a)linutronix.de>
UFS performance for < v4 controllers has reduced quite a bit in 6.16.
This series addresses this regression and brings numbers more or less
back to the previous level.
See patch 2 for some benchmark (fio) results.
Signed-off-by: André Draszik <andre.draszik(a)linaro.org>
---
Changes in v2:
- patch 1: new patch as suggested by Bart during v1 review
- patch 2: update commit message and some inline & kerneldoc comments
- patch 2: add missing jiffies.h include
- Link to v1: https://lore.kernel.org/r/20250724-ufshcd-hardirq-v1-1-6398a52f8f02@linaro.…
---
André Draszik (2):
scsi: ufs: core: complete polled requests also from interrupt context
scsi: ufs: core: move some irq handling back to hardirq (with time limit)
drivers/ufs/core/ufshcd.c | 211 +++++++++++++++++++++++++++++++++-------------
1 file changed, 152 insertions(+), 59 deletions(-)
---
base-commit: 58ba80c4740212c29a1cf9b48f588e60a7612209
change-id: 20250723-ufshcd-hardirq-c7326f642e56
Best regards,
--
André Draszik <andre.draszik(a)linaro.org>
Syzbot reports a KASAN issue as below:
BUG: KASAN: use-after-free in __create_pipe include/linux/usb.h:1945 [inline]
BUG: KASAN: use-after-free in send_packet+0xa2d/0xbc0 drivers/media/rc/imon.c:627
Read of size 4 at addr ffff8880256fb000 by task syz-executor314/4465
CPU: 2 PID: 4465 Comm: syz-executor314 Not tainted 6.0.0-rc1-syzkaller #0
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.14.0-2 04/01/2014
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:88 [inline]
dump_stack_lvl+0xcd/0x134 lib/dump_stack.c:106
print_address_description mm/kasan/report.c:317 [inline]
print_report.cold+0x2ba/0x6e9 mm/kasan/report.c:433
kasan_report+0xb1/0x1e0 mm/kasan/report.c:495
__create_pipe include/linux/usb.h:1945 [inline]
send_packet+0xa2d/0xbc0 drivers/media/rc/imon.c:627
vfd_write+0x2d9/0x550 drivers/media/rc/imon.c:991
vfs_write+0x2d7/0xdd0 fs/read_write.c:576
ksys_write+0x127/0x250 fs/read_write.c:631
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x63/0xcd
The iMON driver improperly releases the usb_device reference in
imon_disconnect without coordinating with active users of the
device.
Specifically, the fields usbdev_intf0 and usbdev_intf1 are not
protected by the users counter (ictx->users). During probe,
imon_init_intf0 or imon_init_intf1 increments the usb_device
reference count depending on the interface. However, during
disconnect, usb_put_dev is called unconditionally, regardless of
actual usage.
As a result, if vfd_write or other operations are still in
progress after disconnect, this can lead to a use-after-free of
the usb_device pointer.
Thread 1 vfd_write Thread 2 imon_disconnect
...
if
usb_put_dev(ictx->usbdev_intf0)
else
usb_put_dev(ictx->usbdev_intf1)
...
while
send_packet
if
pipe = usb_sndintpipe(
ictx->usbdev_intf0) UAF
else
pipe = usb_sndctrlpipe(
ictx->usbdev_intf0, 0) UAF
Guard access to usbdev_intf0 and usbdev_intf1 after disconnect by
checking ictx->disconnected in all writer paths. Add early return
with -ENODEV in send_packet(), vfd_write(), lcd_write() and
display_open() if the device is no longer present.
Set and read ictx->disconnected under ictx->lock to ensure memory
synchronization. Acquire the lock in imon_disconnect() before setting
the flag to synchronize with any ongoing operations.
Ensure writers exit early and safely after disconnect before the USB
core proceeds with cleanup.
Found by Linux Verification Center (linuxtesting.org) with Syzkaller.
Reported-by: syzbot+f1a69784f6efe748c3bf(a)syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=f1a69784f6efe748c3bf
Fixes: 21677cfc562a ("V4L/DVB: ir-core: add imon driver")
Cc: stable(a)vger.kernel.org
Signed-off-by: Larshin Sergey <Sergey.Larshin(a)kaspersky.com>
---
drivers/media/rc/imon.c | 27 ++++++++++++++++++++-------
1 file changed, 20 insertions(+), 7 deletions(-)
diff --git a/drivers/media/rc/imon.c b/drivers/media/rc/imon.c
index f5221b018808..cf3e6e43c0c7 100644
--- a/drivers/media/rc/imon.c
+++ b/drivers/media/rc/imon.c
@@ -536,7 +536,9 @@ static int display_open(struct inode *inode, struct file *file)
mutex_lock(&ictx->lock);
- if (!ictx->display_supported) {
+ if (ictx->disconnected) {
+ retval = -ENODEV;
+ } else if (!ictx->display_supported) {
pr_err("display not supported by device\n");
retval = -ENODEV;
} else if (ictx->display_isopen) {
@@ -598,6 +600,9 @@ static int send_packet(struct imon_context *ictx)
int retval = 0;
struct usb_ctrlrequest *control_req = NULL;
+ if (ictx->disconnected)
+ return -ENODEV;
+
/* Check if we need to use control or interrupt urb */
if (!ictx->tx_control) {
pipe = usb_sndintpipe(ictx->usbdev_intf0,
@@ -949,12 +954,14 @@ static ssize_t vfd_write(struct file *file, const char __user *buf,
static const unsigned char vfd_packet6[] = {
0x01, 0x00, 0x00, 0x00, 0x00, 0xFF, 0xFF };
- if (ictx->disconnected)
- return -ENODEV;
-
if (mutex_lock_interruptible(&ictx->lock))
return -ERESTARTSYS;
+ if (ictx->disconnected) {
+ retval = -ENODEV;
+ goto exit;
+ }
+
if (!ictx->dev_present_intf0) {
pr_err_ratelimited("no iMON device present\n");
retval = -ENODEV;
@@ -1029,11 +1036,13 @@ static ssize_t lcd_write(struct file *file, const char __user *buf,
int retval = 0;
struct imon_context *ictx = file->private_data;
- if (ictx->disconnected)
- return -ENODEV;
-
mutex_lock(&ictx->lock);
+ if (ictx->disconnected) {
+ retval = -ENODEV;
+ goto exit;
+ }
+
if (!ictx->display_supported) {
pr_err_ratelimited("no iMON display present\n");
retval = -ENODEV;
@@ -2499,7 +2508,11 @@ static void imon_disconnect(struct usb_interface *interface)
int ifnum;
ictx = usb_get_intfdata(interface);
+
+ mutex_lock(&ictx->lock);
ictx->disconnected = true;
+ mutex_unlock(&ictx->lock);
+
dev = ictx->dev;
ifnum = interface->cur_altsetting->desc.bInterfaceNumber;
--
2.39.5